Lithographic apparatus and device manufacturing method

ABSTRACT

Apparatus and methods for compensating for the movement of a substrate in a lithographic apparatus during a pulse of radiation include providing a pivotable mirror configured to move a patterned radiation beam incident on the substrate in substantial synchronism with the substrate.

RELATED APPLICATIONS

This application is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 11/371,232 filed Mar. 9, 2006, which is acontinuation-in-part of co-pending U.S. patent application Ser. No.11/297,641 filed Dec. 9, 2005, the entire contents of each of theforegoing applications incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to lithographic projection apparatus andmethods.

BACKGROUND

The term “programmable patterning structure” as here employed should bebroadly interpreted as referring to any configurable or programmablestructure or field that may be used-to endow an incoming radiation beamwith a patterned cross-section, corresponding to a pattern that is to becreated in a target portion of a substrate; the terms “light valve” and“spatial light modulator” (SLM) can also be used in this context.Generally, such a pattern will correspond to a particular functionallayer in a device being created in the target portion, such as anintegrated circuit or other device (see below). Examples of suchpatterning structure include:

-   -   A programmable mirror array. One example of such a device is a        matrix-addressable surface having a viscoelastic control layer        and a reflective surface. The basic principle behind such an        apparatus is that (for example) addressed areas of the        reflective surface reflect incident radiation as diffracted        radiation, whereas unaddressed areas reflect incident radiation        as undiffracted radiation. Using an appropriate filter, the        undiffracted radiation can be filtered out of the reflected        beam, leaving only the diffracted radiation behind; in this        manner, the beam becomes patterned according to the addressing        pattern of the matrix-addressable surface. An array of grating        light valves (GLVs) may also be used in a corresponding manner,        where each GLV may include a plurality of reflective ribbons        that can be deformed relative to one another (e.g., by        application of an electric potential) to form a grating that        reflects incident radiation as diffracted radiation. A further        alternative embodiment of a programmable mirror array employs a        matrix arrangement of very small (possibly microscopic) mirrors,        each of which can be individually tilted about an axis by        applying a suitable localized electric field, or by employing        piezoelectric actuation means. For example, the mirrors may be        matrix-addressable, such that addressed mirrors will reflect an        incoming radiation beam in a different direction to unaddressed        mirrors; in this manner, the reflected beam is patterned        according to the addressing pattern of the matrix-addressable        mirrors. The required matrix addressing can be performed using        suitable electronic means. In both of the situations described        hereabove, the patterning structure can comprise one or more        programmable mirror arrays. More information on mirror arrays as        here referred to can be gleaned, for example, from U.S. Pat.        Nos. 5,296,891 and 5,523,193 and PCT Patent Application Nos. WO        98/38597 and WO 98/33096, which documents are incorporated        herein by reference. In the case of a programmable mirror array,        the support structure may be embodied as a frame or table, for        example, which may be fixed or movable as required.    -   A programmable LCD array. An example of such a construction is        given in U.S. Pat. No. 5,229,872, which is incorporated herein        by reference. As above, the support structure in this case may        be embodied as a frame or table, for example, which may be fixed        or movable as required.

It should be appreciated that where pre-biasing of features, opticalproximity correction features, phase variation techniques, and/ormultiple exposure techniques are used, the pattern “displayed” on theprogrammable patterning structure may differ substantially from thepattern eventually transferred to the substrate or layer thereof.

Lithographic projection apparatus can be used, for example, in themanufacture of integrated circuits (ICs), flat panel displays, and otherdevices involving fine structures. In such a case, the programmablepatterning structure may generate a circuit pattern corresponding to anindividual layer of, for example, the IC, and this pattern can be imagedonto a target portion (e.g., comprising one or more dies and/orportion(s) thereof) on a substrate (e.g., a glass plate or a wafer ofsilicon or other semiconductor material) that has been coated with alayer of radiation-sensitive material (e.g., resist). In general, asingle substrate will contain a whole matrix or network of adjacenttarget portions that are successively irradiated via the projectionsystem (e.g., one at a time).

The lithographic projection apparatus may be of a type commonly referredto as a step-and-scan apparatus. In such an apparatus, each targetportion may be irradiated by progressively scanning the mask patternunder the beam in a given reference direction (the “scanning” direction)while substantially synchronously scanning the substrate table parallelor anti-parallel to this direction. Since, in general, the projectionsystem will have a magnification factor M (generally<1), the speed V atwhich the substrate table is scanned will be a factor M times that atwhich the mask table is scanned. A beam in a scanning type of apparatusmay have the form of a slit with a slit width in the scanning direction.More information with regard to lithographic devices as here describedcan be gleaned, for example, from U.S. Pat. No. 6,046,792, which isincorporated herein by reference.

In a manufacturing process using a lithographic projection apparatus, apattern (e.g., in a mask) is imaged onto a substrate that is at leastpartially covered by a layer of radiation-sensitive material (e.g.,resist). Prior to this imaging procedure, the substrate may undergovarious other procedures such as priming, resist coating, and/or a softbake. After exposure, the substrate may be subjected to other proceduressuch as a post-exposure bake (PEB), development, a hard bake, and/ormeasurement/inspection of the imaged features. This set of proceduresmay be used as a basis to pattern an individual layer of a device (e.g.,an IC). For example, these transfer procedures may result in a patternedlayer of resist on the substrate. One or more pattern processes mayfollow, such as deposition, etching, ion-implantation (doping),metallization, oxidation, chemo-mechanical polishing, etc., each ofwhich may be intended to create, modify, or finish an individual layer.If several layers are required, then the whole procedure, or a variantthereof, may be repeated for each new layer. Eventually, an array ofdevices will be present on the substrate (wafer). These devices are thenseparated from one another by a technique such as dicing or sawing,whence the individual devices can be mounted on a carrier, connected topins, etc. Further information regarding such processes can be obtained,for example, from the book “Microchip Fabrication: A Practical Guide toSemiconductor Processing,” Third Edition, by Peter van Zant, McGraw HillPublishing Co., 1997, ISBN 0-07-067250-4.

The term “projection system” should be broadly interpreted asencompassing various types of projection system, including refractiveoptics, reflective optics, catadioptric systems, and micro lens arrays,for example. It is to be understood that the term “projection system” asused in this application simply refers to any system for transferringthe patterned beam from the programmable patterning structure to thesubstrate. For the sake of simplicity, the projection system mayhereinafter be referred to as the “projection lens.” The radiationsystem may also include components operating according to any of thesedesign types for directing, shaping, reducing, enlarging, patterning,and/or otherwise controlling the beam of radiation, and such componentsmay also be referred to below, collectively or singularly, as a “lens.”

Further, the lithographic apparatus may be of a type having two or moresubstrate tables (and/or two or more mask tables). In such “multiplestage” devices the additional tables may be used in parallel, orpreparatory steps may be carried out on one or more tables while one ormore other tables are being used for exposures. Dual stage lithographicapparatus are described, for example, in U.S. Pat. No. 5,969,441 and PCTApplication No. WO 98/40791, which documents are incorporated herein byreference.

The lithographic apparatus may also be of a type wherein the substrateis immersed in a liquid having a relatively high refractive index (e.g.,water) so as to fill a space between the final element of the projectionsystem and the substrate. Immersion liquids may also be applied to otherspaces in the lithographic apparatus, for example, between the mask andthe first element of the projection system. The use of immersiontechniques to increase the effective numerical aperture of projectionsystems is known in the art.

In the present document, the terms “radiation” and “beam” are used toencompass all types of electromagnetic radiation, including ultravioletradiation (e.g., with a wavelength of 365, 248, 193, 157 or 126 nm) andEUV (extreme ultra-violet radiation, e.g., having a wavelength in therange 5-20 nm), as well as particle beams (such as ion beams or electronbeams).

In presently known lithographic projection apparatus using programmablepatterning structure, the substrate table is scanned in the path of thepatterned radiation beam (e.g., below the programmable patterningstructure). A pattern is set on the programmable patterning structureand is then exposed on the substrate during a pulse of the radiationsystem. In the interval before the next pulse of the radiation system,the substrate table moves the substrate to a position as required toexpose the next target portion of the substrate (which may include allor part of the previous target portion), and the pattern on theprogrammable patterning structure is updated if necessary. This processmay be repeated until a complete line (e.g., row of target portions) onthe substrate has been scanned, whereupon a new line is started.

During the small but finite time that the pulse of the radiation systemlasts, the substrate table may consequently have moved a small butfinite distance. Previously, such movement has not been a problem forlithographic projection apparatus using programmable patterningstructure, e.g., because the size of the substrate movement during thepulse has been small relative to the size of the feature being exposedon the substrate. Therefore the error produced was not significant.However, as the features being produced on substrates become smaller,such error becomes more significant. U.S. Publication Application No.2004/0141166 proposes one solution to this problem.

Although specific reference may be made in this text to the use of theapparatus according to an embodiment of the invention in the manufactureof ICs, it should be explicitly understood that such an apparatus hasmany other possible applications. For example, it may be employed in themanufacture of integrated optical systems, guidance and detectionpatterns for magnetic domain memories, liquid-crystal display (LCD)panels, thin-film magnetic heads, thin-film-transistor (TFT) LCD panels,printed circuit boards (PCBs), DNA analysis devices, etc. The skilledartisan will appreciate that, in the context of such alternativeapplications, any use of the terms “wafer” or “die” in this text shouldbe considered as being replaced by the more general terms “substrate”and “target portion”, respectively.

SUMMARY

According to an embodiment of the invention, there is provided alithographic projection apparatus, comprising a projection systemconfigured to project a patterned radiation beam onto a target portionof a substrate; a positioning structure configured to move the substraterelative to the projection system during exposure by the patternedradiation beam; a pivotable mirror configured to move the patternedradiation beam relative to the projection system during at least onepulse of the patterned radiation beam; and an actuator configured tooscillatingly pivot the mirror according to an oscillation timing thatsubstantially corresponds to a pulse frequency of a radiation system andsuch that the patterned radiation beam is scanned in substantialsynchronism with the movement of the substrate during the at least onepulse.

According to an embodiment of the invention, there is provided a devicemanufacturing method, comprising: providing a pulsed beam of radiation;patterning the pulsed beam of radiation according to a desired pattern;projecting the patterned radiation beam onto a target portion of a layerof radiation-sensitive material that at least partially covers asubstrate; moving the substrate relative to a projection system thatprojects the patterned radiation beam onto the substrate duringexposure; and oscillatingly pivoting a pivotable mirror according to anoscillation timing that substantially corresponds to a pulse frequencyof the patterned radiation beam, so as to alter a path of the patternedradiation beam relative to the projection system during at least onepulse of the patterned radiation beam, wherein the path is altered insubstantial synchronism with the movement of the substrate during the atleast one pulse and wherein a cross-section of the patterned radiationbeam is projected onto a plane substantially parallel to a surface ofthe target portion of the substrate.

According to an embodiment of the invention, there is provided a devicemanufacturing method, comprising: moving a substrate relative to aprojection system that projects a patterned radiation beam onto asubstrate during exposure; oscillatingly pivoting a pivotable mirroraccording to an oscillation timing that substantially corresponds to apulse frequency of the patterned radiation beam so as to alter a path ofthe patterned radiation beam in substantial synchronism with movement ofthe substrate; and projecting the patterned radiation beam onto thesubstrate.

According to an embodiment, there is provided a lithographic apparatuscomprising:

-   -   an illumination system configured to condition a radiation beam;    -   a support constructed to hold a patterning device, the        patterning device configured to impart the radiation beam with a        pattern in its cross-section to form a patterned radiation beam;    -   a substrate table constructed to hold a substrate;    -   a projection system configured to project the patterned        radiation beam onto a target portion of the substrate;    -   a position measurement system configured to measure a position        of the patterning device, or of the support, or of both the        patterning device and the support;    -   a position measurement system configured to measure a position        of the substrate, or of the substrate table, or of both the        substrate and the substrate table; and    -   a radiation beam position adjuster configured to adjust a        position of the patterned beam of radiation projected onto the        substrate, relative to the position of the projection system, in        response to a deviation of the measured relative position of the        patterning device and the substrate from an intended relative        position of the patterning device and the substrate.

According to an embodiment, there is provided a device manufacturingmethod, comprising:

-   -   patterning a beam of radiation with a patterning device;    -   projecting the patterned beam of radiation, using a projection        system, onto a target portion of a substrate to form an        exposure;    -   measuring the position of the patterning device, of a support        holding the patterning device, or of both the patterning device        and the support, during the exposure;    -   measuring the position of the substrate, of a table holding the        substrate, or of both the substrate and the table, during the        exposure; and    -   adjusting a position of the patterned beam of radiation        projected onto the substrate, relative to the projection system,        in response to a deviation of the measured relative position of        the patterning device and the substrate from an intended        relative position of the patterning device and the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying schematic drawings inwhich:

FIG. 1 depicts a lithographic projection apparatus according to anembodiment of the invention;

FIG. 2 schematically depicts a structure configured to move thepatterned radiation beam according to an embodiment of the presentinvention;

FIG. 3 schematically depicts a structure configured to move thepatterned radiation beam after a partial movement of the structure;

FIG. 4 schematically depicts a structure configured to move thepatterned radiation beam after further movement of the structure;

FIG. 5 schematically depicts an example of a control loop that may beused to control the movement of the structure;

FIG. 6 schematically depicts a variant of a structure configured to movethe patterned radiation beam;

FIG. 7 schematically depicts a control system according to a particularembodiment of the present invention;

FIG. 8 schematically depicts a control system according to a differentparticular embodiment of the present invention;

FIG. 9 schematically depicts a flexible support that may be used with aparticular embodiment of the present invention; and

FIG. 10 schematically depicts an application of an embodiment of thepresent invention to a lithographic apparatus utilizing a mask topattern a beam of radiation.

In the Figures, corresponding reference symbols indicate correspondingparts.

DETAILED DESCRIPTION

Embodiments of the invention include, for example, methods and apparatusthat may be used to reduce errors caused by movement of the substrateduring a pulse of the radiation system.

FIG. 1 schematically depicts a lithographic projection apparatus 1according to a particular embodiment of the invention. The apparatuscomprises:

-   -   a radiation system configured to supply (e.g., having structure        capable of supplying) a beam of radiation. In this particular        example, the radiation system Ex, IL, for supplying a beam PB of        radiation (e.g., UV or EUV radiation) also comprises a radiation        source LA;    -   a programmable patterning structure PPM (e.g., a programmable        mirror array) configured to apply a pattern to the beam. In        general, the position of the programmable patterning structure        will be fixed relative to projection system PL. However, it may        instead be connected to a positioning structure configured to        accurately position it with respect to projection system PL;    -   an object table (substrate table) WT configured to hold a        substrate. In this example, substrate table WT is provided with        a substrate holder for holding a substrate W (e.g., a        resist-coated semiconductor wafer) and is connected to a        positioning structure PW for accurately positioning the        substrate with respect to projection system PL and (e.g.,        interferometric) measurement structure IF, which is configured        to accurately indicate the position of the substrate and/or        substrate table with respect to projection system PL; and    -   a projection system (“projection lens”) PL (e.g., a quartz        and/or CaF₂ projection lens system, a catadioptric system        comprising lens elements made from such materials, and/or a        mirror system) configured to project the patterned beam onto a        target portion C (e.g., comprising one or more dies and/or        portion(s) thereof) of the substrate W. The projection system        may project an image of the programmable patterning structure        onto the substrate.

As here depicted, the apparatus is of a reflective type (e.g., has areflective programmable patterning structure). However, in general, itmay also be of a transmissive type (e.g., with a transmissiveprogrammable patterning structure) or have aspects of both types.

The source LA (e.g., a mercury lamp, an excimer laser, an electron gun,a laser-produced plasma source or discharge plasma source, or anundulator provided around the path of an electron beam in a storage ringor synchrotron) produces a beam of radiation. This beam is fed into anillumination system (illuminator) IL, either directly or after havingtraversed a conditioning structure or field, such as a beam expander Ex,for example. The illuminator IL may comprise an adjusting structure orfield AM for setting the outer and/or inner radial extent (commonlyreferred to as σ-outer and σ-inner, respectively) of the intensitydistribution in the beam, which may affect the angular distribution ofthe radiation energy delivered by the beam at, for example, thesubstrate. In addition, the apparatus will generally comprise variousother components, such as an integrator IN and a condenser CO. In thisway, the beam PB impinging on the programmable patterning structure PPMhas a desired uniformity and intensity distribution in itscross-section.

It should be noted with regard to FIG. 1 that the source LA may bewithin the housing of the lithographic projection apparatus (as is oftenthe case when the source LA is a mercury lamp, for example), but that itmay also be remote from the lithographic projection apparatus, theradiation beam which it produces being led into the apparatus (e.g.,with the aid of suitable direction mirrors); this latter scenario isoften the case when the source LA is an excimer laser. The one or moreembodiments of the invention and the claims encompass both of thesescenarios. In a typical source LA, there are a number of effects thatcan result in imaging errors in a lithographic imaging processes. In anembodiment wherein the source LA provides pulsed radiation, forinstance, these may include pulse amplitude variation, pulse-widthvariation, and pulse-to-pulse variation, also known as jitter.

The beam PB subsequently intercepts the programmable patterningstructure PPM, which may be held on a mask table (not shown). Havingbeen selectively reflected by (alternatively, having traversed) theprogrammable patterning structure PPM, the beam PB passes through theprojection system PL, which focuses the beam PB onto a target portion Cof the substrate W. In the embodiment of FIG. 1, a beam splitter BSserves to direct the beam to the patterning structure PPM, while alsoallowing it to pass through to the projection system PL, howeveralternate geometries are within the scope of one or more embodiments ofthe present invention. It should be appreciated that although anembodiment of the present invention is described herein in relation to alithographic apparatus incorporating a programmable patterning structureto impart a pattern to a beam of radiation, the invention is not limitedto such an arrangement. In particular, an embodiment of the inventionmay be used in conjunction with a lithographic apparatus in which amask, for example held on a mask table, is used to impart a pattern tothe beam of radiation.

With the aid of the positioning structure (and interferometric measuringstructure IF), the substrate table WT can be moved accurately, e.g., soas to position different target portions C in the path of the beam PB.Where used, a positioning structure for the programmable patterningstructure PPM can be used to accurately position the programmablepatterning structure PPM with respect to the path of the beam PB (e.g.,after a placement of the programmable patterning structure PPM, betweenscans, and/or during a scan).

In general, movement of the object table WT may be realized with the aidof a long-stroke module (e.g., for coarse positioning) and ashort-stroke module (e.g., for fine positioning), which are notexplicitly depicted in FIG. 1. A similar system may be used to positionthe programmable patterning structure PPM. It will be appreciated that,to provide the required relative movement, the beam may alternatively oradditionally be moveable, while the object table and/or the programmablepatterning structure PPM may have a fixed position. Programmablepatterning structure PPM and substrate W may be aligned using substratealignment marks P1, P2 (possibly in conjunction with alignment marks ofthe programmable patterning structure PPM).

The depicted apparatus can be used in several different modes. In onescan mode, the mask table is movable in a given direction (the so-called“scan direction,” e.g., the y direction) with a speed v, so that thebeam PB is caused to scan over a mask image. Concurrently, the substratetable WT is simultaneously moved in the same or opposite direction at aspeed V=Mv, in which M is the magnification of the projection system PL(typically, M=¼ or ⅕). In some embodiments, the demagnification issignificantly smaller than 1, for example smaller than 0.3, smaller than0.1, smaller than 0.05, smaller than 0.01, smaller than 0.005, orsmaller than 0.0035. Likewise, it is contemplated that M may be largerthan 0.001, or may be within a range between 0.001 and the foregoingupper limits. In this manner, a relatively large target portion C can beexposed, without having to compromise on resolution.

In another mode, the mask table is kept essentially stationary holding aprogrammable patterning structure, and the substrate table WT is movedor scanned while a pattern imparted to the beam is projected onto atarget portion C. In this mode, generally a pulsed radiation source isemployed and the programmable patterning structure is updated asrequired after each movement of the substrate table WT or in betweensuccessive radiation pulses during a scan. This mode of operation can bereadily applied to lithography that utilizes programmable patterningstructure, such as a programmable mirror array as referred to above.

Combinations and/or variations on the above-described modes of use orentirely different modes of use may also be employed.

An apparatus as depicted in FIG. 1 may be used, for example, in thefollowing manner. In pulse mode, the programmable patterning structurePPM is kept essentially stationary, and the entire pattern is projectedonto a target portion C of the substrate using a pulsed radiationsource. The substrate table WT is moved with an essentially constantspeed such that the beam PB is caused to scan a line across thesubstrate W. The pattern on the programmable patterning structure PPM isupdated as required between pulses of the radiation system, and thepulses are timed such that successive target portions C are exposed atthe required locations on the substrate W. Consequently, the beam PB canscan across the substrate W to expose the complete pattern for a stripof the substrate. Such a process may be repeated until the completesubstrate W has been exposed line by line. Different modes may also beused.

Because of the relative motion of the substrate table during imaging,changes in the time domain at the radiation source LA map to changes inthe spatial domain at the substrate table WT. This results in two maineffects. First, when there is a change in the pulse interval, there is achange in imaged position on the substrate. For example, a pulseinterval that is slightly longer than average results in a greaterdistance between imaged portions of the substrate. Second, a change inpulse duration results in a blurring effect, as a longer or shorterportion of the substrate traverses the image field during the pulse.

In order to account for the movement of the substrate table WT, a devicein accordance with an embodiment of the present invention may include amirror 10 forming a part of the projection system PL, as shown in FIG.2. In particular, the mirror 10 is beneficially located proximate apupil of the projection system PL or at a conjugate plane thereof.Though FIG. 2 shows the projection system PL as a two-part device, withthe mirror 10 bisecting the projection system PL, that is not, ingeneral, a requirement of one or more embodiments of the presentinvention. To the contrary, the specific arrangement of the projectionsystem PL may be varied as required according to other desired imagingcharacteristics. As will be appreciated, the mirror 10 should besubstantially planar, though in practice it may be possible to allow forsome curvature, whereby a portion of the optical power of the projectionsystem resides in the mirror.

An actuator, or group of actuators, 12 is positioned to move the mirror10 during an imaging operation. In a particular embodiment, the actuator12 may be arranged to reciprocally rotate the mirror 10 about a smallangle at a relatively high frequency, namely to oscillatingly pivot themirror. In particular the rotation may be about an axis that lies withthe plane of reflection of the mirror.

The system of FIG. 2 is shown as having a 1:1 magnification ratio, and arelatively large rotation of the mirror 10. As a result, the focal point14 at the image plane 16 is displaced from the optical axis 18 by arelatively large amount d. In practice, there may be a significantde-magnification, and the tilt of the mirror 10 will be quite small, sothat the displacement may then be quite small. In particular, thedisplacement of the image should correspond substantially to a distancetraversed by the substrate table over the duration of a single pulse ofthe radiation source.

By way of example, a displacement at the mirror 10 of 1 nm at theposition of a marginal ray maps to a displacement at the image plane 16of 1/NA, where NA is the numerical aperture of the projection system PL.Likewise, the rotational change of the mirror a′ [in rad/s] thattranslates over the diameter of the beam at the pupil D [in m] equals toa velocity v at substrate level [in m/s] as follows: v=a′D/(2NA).

FIGS. 3 and 4 illustrate schematically later times in a single scan, assuccessive pulses are imaged onto the focal plane. In FIG. 3, the mirror10 has rotated through to its zero-crossing, and the focal point 14 isaligned with the optical axis 18. FIG. 4 continues the motion and thefocal point 14 is once more displaced from the optical axis 18, in adirection opposite to its initial displacement of FIG. 2.

In a typical lithographic apparatus, the source LA may have a pulserepetition rate on the order of 1-10 kHz. As a result, it is useful toensure that the mirror 10 can be adequately vibrated in phase with thatfrequency, meaning that the actuator or actuators 12 should be adaptedfor high frequency operation. Furthermore, if the mirror 10 is designedso that, along with its associated mounting structure, it has a resonantfrequency that is substantially equal to the pulse frequency of thesource LA, energy required to move the mirror should be minimized. Thishas the additional effect that the load on the actuators andconsequently the deformation load on the mirror 10 should be minimized.

In furtherance of the goal of matching the frequency of the vibration ofthe mirror 10 with the pulse frequency of the source LA, it is possibleto include a sensor 30 that is connected in a control loop with themirror 10, its actuator(s) 12 and, if required, the substrate table. Forsynchronization of the movement of the mirror to the source pulsefrequency, different methods may be used. By way of example, a signalfrom the sensor 30 on the vibrating mirror may be used to trigger thesource pulse, or a phase locked loop system may be used where the sourcefrequency is fixed to the average resonant frequency of the mirror whilethe controller adjusts the mirror frequency and phase to the fixedsource frequency. As a further example, an external timing source may beprovided that both triggers the source pulse and is used to control boththe phase and amplitude of the mirror motion.

In addition to ensuring that the frequency of vibration of the mirror 10is substantially synchronized with the frequency of the source LA, itmay be beneficial to ensure that the amplitude A of the rotationalvelocity of the mirror 10 corresponds to a scan speed of the substratetable.

Further by way of example, in a typical system, the actual values may beas follows. The scan speed may be on the order of 10 mm/s, NA=1, andD=20 mm. This leads to a′=1 rad/s at the zero-crossing of a sinusoidalrotational movement of the mirror 10. Given that for a sinusoidalmovement a=A sin(2πtv)) where A is the amplitude in rad, so the timederivative equals: a′=A2πv cos(2πtv)). At t=0 this becomes: a′=A2πv sothat for a 1 kHz vibration, the amplitude of the movement of the mirrorbecomes: A=0.16 mrad.

The choice of a sinusoidal rotational motion of the mirror may allow forsome useful effects. In particular, by choosing a portion of the motionclose to the zero crossing to coincide with the imaging pulse, and asmall amplitude, the sinusoidal motion is substantially linear.Furthermore, the gradual deceleration and acceleration at the end pointsof the motion reduce stresses on the mirror, which, if unchecked, couldlead to deformations of the mirror over time. It should be appreciated,however, that one or more embodiments of the invention are not limitedto the use of a sinusoidal rotation motion.

The mirror may also be coupled to one or more balance masses. The one ormore balance masses are configured to take up and isolate forcesproduced by the actuator in vibrating the mirror. In particular, the oneor more balance masses are configured to be freely moveable in adirection opposite to the forces generated by the actuator, conservingmomentum of the balance mass-mirror system and thereby reducing forcesintroduced into other portions of the lithographic apparatus.

Although, as discussed above, the resonant frequency of the mirrorassembly (namely the combination of the mirror, its associated mountingstructure and the actuator system that drives it) may be set to matchthe pulse frequency of the source LA, in practice this may be difficultto precisely achieve. For example, due to manufacturing tolerances orthermal effects during operation, the resonant frequency of the assemblymay vary by as much as 1%. In addition, the frequency of the source LAmay vary in operation, resulting in a requirement to operate the mirrorat a frequency other than precisely its resonant frequency. For someconfigurations, relatively large damping may be expected.

Consequently, if one wishes to use a phase locked loop (PLL) or positionservo control in order to control the oscillation of the mirror, thecontroller may need to operate at a frequency that is multiple timesthat of the frequency of oscillation of the mirror. For example, if thesource has a pulse frequency of 6 KHz, the mirror will havesubstantially the same frequency and the controller for the mirror mayhave a frequency of, for example, 60 KHz. It should be appreciated thatthe sampling frequency should be an integer multiple of the desiredoscillation frequency in order to avoid unwanted harmonics.

In an embodiment of the invention, a control system such as thatrepresented in FIG. 7 is provided. In this arrangement, a referencesignal, corresponding to the desired frequency of oscillation, phase andamplitude of the motion of the mirror is generated by a signal generator40. The signal is then modified by a phase compensator 41 and anamplitude compensator 42 to produce a phase and amplitude compensatedsignal 43. This compensated signal is supplied to the actuator system44, resulting in the oscillation of the mirror 45. A sensor 46 is usedto measure the actual motion of the mirror.

Subsequently, a phase and amplitude calculation unit 47 determines thedifference between the actual motion of the mirror and the intendedmotion of the mirror as represented by the reference signal generated bythe signal generator 40. From this, the phase and amplitude calculationunit 47 determines the phase difference between the intended and actualmovement of the mirror and the difference between the intended and theactual amplitude of motion of the mirror. These differences are fed backto the phase compensator 41 and the amplitude compensator 42,respectively, in order to generate the phase and amplitude compensatedsignal 43. Advantageously, although the reference signal generator 40and the sensor 46 that measures the movement of the mirror useelectronics that function at multiple times the oscillation frequency ofthe mirror, the phase and amplitude calculation unit 47, the phasecompensator 41 and the amplitude compensator 42 need not operate at sucha high frequency. Accordingly, the cost of the control system may bereduced. However, in practice, at least a part of the phase andamplitude calculation unit 47 may operate at the higher samplingfrequency.

FIG. 8 depicts a control system for the mirror motion according toanother particular embodiment of the present invention. As before, asignal generator 50 generates a reference signal that represents thedesired motion of the mirror. An amplitude compensator 51 adjusts theamplitude of the signal to provide an amplitude compensated signal 52that is provided to the actuator system 53, resulting in the oscillationof the mirror 54. As before, a sensor 55 is used to measure the motionof the mirror and a phase and amplitude calculation unit 56 measures thephase and amplitude difference between the actual motion of the mirrorand the intended motion as represented by the reference signal generatedby the signal generator 50.

As with the embodiment discussed above in relation to FIG. 7, the phaseand amplitude calculation unit 56 determines the difference between theintended and actual phase and amplitude of the motion of the mirror andfeeds back the amplitude difference to the amplitude compensator 51 foruse in generating the amplitude compensated signal 52. However, in thisparticular embodiment, the phase difference between the intended andactual motion of the mirror is used by a phase compensator 57 todetermine a needed change in the resonant frequency of the mirrorassembly. This is provided to a resonant frequency adjustment unit 58which adjusts the resonant frequency of the mirror assembly such thatthe phase difference between the intended and actual motion of themirror is reduced.

As with the embodiment discussed above in relation to FIG. 7, althoughthe reference signal generator 50 and the sensor 55 operate at afrequency that is multiple times that of the frequency of oscillation ofthe mirror, the remainder of the control system may operate at a lowerfrequency. Accordingly, the cost of the control system may be reduced.Advantageously, because in this embodiment the resonant frequency of themirror assembly is adjusted to match the desired frequency ofoscillation, the magnitude of the drive signal that is supplied to theactuator system of the mirror assembly may be greatly reduced. In thisrespect, the magnitude of the drive signal is not only affected by thedamping within the mirror assembly but also by the magnitude of thedifference between the intended oscillation frequency of the mirrorassembly and the natural resonant frequency. It may be beneficial toreduce the magnitude of the drive signal for the mirror assembly becausethe mirror assembly may be mounted within the projection system. Thegreater the magnitude of the drive signal provided to the mirrorassembly, the greater the amount of heat that may be generated withinthe mirror assembly and that may have a detrimental affect on theaccuracy of the projection system.

The resonant frequency of the mirror assembly may be adjusted byproviding a system by which a fluid or another material, such as metalshavings, can be controllably added to or removed from the mirrorassembly in order to adjust its mass (i.e., to or from a chamber in oron the mirror or any other portion of the mirror assembly).Alternatively or additionally, the resonant frequency may be adjusted bychanging the stiffness of the mirror assembly. The latter avoids anycomplications that may result from, for example, a change of thelocation of the center of gravity of the mirror assembly by the additionand/or removal of mass from the mirror assembly.

FIG. 9 depicts an arrangement by which the stiffness of the mirrorassembly may be adjusted. In particular, FIG. 9 depicts a flexible mount60 that may be used to mount the mirror 61 to a reference 62 within theapparatus, such as a reference frame or base frame of the apparatus. Theflexible mount 60 includes a chamber 63 that is filled with amagneto-rheological (MR) fluid. Adjacent the chamber 63 are one or moreelectromagnets 64, connected to a controller 65. One of the propertiesof magneto-rheological fluids is that the viscosity, and hencestiffness, of the fluid changes as a function of a magnetic fieldapplied to the fluid. Accordingly, by adjusting the magnetic fieldapplied to the magneto-rheological fluid within the chamber 63, thestiffness of the flexible support 60 may be adjusted. Adjusting thestiffness of one or more such flexible supports 60 may be used to adjustthe stiffness of the mirror assembly overall. Any other mechanism toadjust the stiffness of the mirror assembly may also be used.

Embodiments of the present invention can provide the ability to increasepulse time as a result of decreasing blur associated with movement ofthe substrate table. One useful result of increased pulse time is theability to reduce peak intensity, without reducing a total energy perpulse, thereby reducing potential damage to optical components. Anotheruseful result is that the number of temporal modes may increase, therebyreducing speckle in the optical system. Finally, longer pulse times mayallow for the ability to truncate individual pulses, thereby allowingfor pulse-to-pulse dose control adjustments.

Errors caused by the movement of the substrate relative to theprojection system during a pulse of radiation may be reduced byproviding one or more apparatus to shift the patterned radiation beam insubstantial synchronism with the movement of the substrate during apulse of radiation, which may allow the radiation beam to remain moreaccurately aligned on the substrate. Alternative structures that may beapplied to shift the patterned radiation beam are also within the scopeof one or more embodiments of the invention.

In particular, it is possible to compensate for an error of movement ofthe substrate relative to the projection system during a pulse ofradiation. Such an error is a deviation, for example, from an intendedmotion of the substrate relative to the projection system, for examplethe substrate scanning relative to the projection system at asubstantially constant speed. This deviation from the intended movementmay be caused by an imperfection in the system used to control themovement of the substrate, for example cogging or a motor force factorvariation within an actuator used to control the position of thesubstrate and/or a vibration that may be transferred to the substratefrom other components within the lithographic apparatus.

The deviation of the movement of the substrate relative to theprojection system from the intended movement of the substrate may bederived from the output of a sensor configured to measure the positionor displacement of the substrate or a support on which the substrate isheld.

The difference between the intended position of the substrate and theactual position of the substrate corresponds to a required change ofposition of the mirror 10. Accordingly, the actuator(s) 12 may beconfigured to control the movement of the mirror 10 by a combination ofthe movement required to oscillate the mirror in substantial synchronismwith the pulse rate of the source LA such that the patterned radiationbeam scans in substantial synchronism with the intended position of thesubstrate plus a correction in order to compensate for the deviation ofthe movement of the substrate relative to its intended movement.

The correction of the movement of the mirror 12 to compensate for adeviation from the intended movement of the substrate may be effected byadjusting the mid-point of the oscillation of the mirror 10.Alternatively or additionally, the adjustment may be effected bycontrolling a phase difference between the oscillation of the mirror 10and the pulsing of the radiation source LA.

Alternatively or additionally, as depicted in FIG. 6, one or more secondactuators 20 may be provided that provides the adjustment of theposition of the mirror 10, corresponding to the correction required tocompensate for the deviation of the movement of the substrate from itsintended movement, by adjusting the position of the actuator(s) 12. Forexample, the actuator(s) 12 may control the position of the mirror 10relative to a base 12 a of the actuator(s) 12. The second actuator(s) 20may therefore be configured to control the position of the base 12 a ofthe actuator(s) 12 relative to a reference within the lithographicapparatus. Accordingly, the actuator(s) 12 is used to control theoscillation of the mirror 10 such that the patterned radiation beam isscanned in substantial synchronism with the intended motion of thesubstrate and the second actuator(s) 20 is used in order to provide anynecessary correction for deviation of the substrate from its intendedmovement.

Regardless of how the corrections are applied to the motion of themirror 10, it should be appreciated that the corrections may be appliedin order to rotate the mirror about the same axis as the axis aboutwhich the mirror oscillates. Alternatively or additionally, thecorrections may be applied to rotate the mirror about an axis lyingwithin a plane substantially parallel to the surface of the mirror atthe location on which the patterned radiation beam is incident on themirror, but perpendicular to the axis about which the mirror oscillates.Accordingly, the corrections may adjust for deviations from the intendedmovement of the substrate in a direction parallel and/or perpendicularto, respectively, the scanning motion of the substrate.

One or both of the actuator(s) 12 and the second actuators 20 may beformed from any suitable actuator or a combination thereof. Inparticular, one or more piezo-electric elements may be used as theactuator(s) 12,20. As an alternative, one or both of the actuator(s) maybe a Lorentz actuator. An advantage of such an arrangement is that itmay be arranged to minimize the transfer of vibration from one componentto the other. Accordingly, the second actuator(s) 20 may, in particular,be a Lorentz actuator and configured to minimize the transfer ofvibrations from the actuator(s) 12, that oscillates the mirror 10, tothe remainder of the apparatus.

In general, it should be appreciated that one or both of the actuator(s)12,20 may be able to adjust the position of the mirror in up to sixdegrees of freedom.

It may be desirable to move the substrate at a substantially constantvelocity relative to the projection system during a series of pulses ofthe radiation system and the intervals in between the pulses. Anapparatus as described herein may then be used to move the patternedradiation beam in substantial synchronism with the movement of thesubstrate for the duration of at least one pulse of the radiationsystem. Having the substrate moving at a substantially constant velocitymay reduce the complexity of the substrate table and the positionaldrivers associated with it, and moving the patterned radiation beam insubstantial synchronism with the movement of the substrate may reduceconsequent errors.

The patterned radiation beam may be moved in substantial synchronismwith the movement of the substrate during a plurality of pulses. Such anarrangement may enable the images of the programmable patterningstructure to be projected onto the same part of the substrate aplurality of times. This technique may be done, for example, if theintensity of the pulse of the patterned radiation beam is not sufficientto produce a complete exposure on the substrate. Moving the patternedradiation beam in substantial synchronism with the substrate may reducethe occurrence of overlay errors between subsequent exposures of thepattern on the substrate.

Successive patterns on the programmable patterning structure that areexposed on the substrate by each pulse may be different. For example,one or more corrections may be made in one or more subsequent pulses tooffset an error in a first pulse. Alternatively, a change in the patternmay be used to produce a gray scale image for one or more of thefeatures (for example, by only exposing those features for a proportionof the total number of pulses imaged onto a given part of thesubstrate).

Additionally or alternatively, the intensity of the patterned radiationbeam, the illumination of the programmable patterning structure, and/orthe pupil filtering may be changed for one or more of the pulses of theradiation system that are projected onto the same part of the substrate.This technique may be used, for example, to increase the number of grayscales that may be generated using the technique described in thepreceding paragraph or may be used to optimize different exposures forfeatures oriented in different directions.

Although the arrangement discussed above has been described in relationto compensating for a deviation from the intended movement of asubstrate in a lithographic apparatus using a programmable patterningstructure, it should be appreciated that the concept may also be appliedto an apparatus in which a pattern is applied to a beam of radiation bymeans of, e.g., a mask. In such a situation, the mask may be arranged ona support such that it can be scanned relative to a beam of radiationprojected onto it in synchronism with the movement of the substraterelative to the beam of radiation patterned by the mask. In such asituation, the movement of the substrate should accurately reflect themovement of the mask. However, where an error in the relative movementof the substrate and the mask occur, such an error may be compensated byusing an adjustable mirror that adjusts the position of the beam ofradiation projected onto the substrate relative to the projection systemin the same manner as discussed above. It should be appreciated,however, that in this case only the corrective movement of the mirror isused and the elements of the system used to provide the oscillation ofthe mirror in synchronism with the pulses of the radiation system andthe updating of the pattern on the programmable patterning structure, asdiscussed above, are not needed. It should further be appreciated thatwhere the projection system is configured to demagnify the image of themask that is projected onto the substrate by a given factor, thecorresponding movement of the substrate is reduced by the same factorcompared to the movement of the mask.

FIG. 10 depicts such a lithographic apparatus. It includes a source ofradiation 70, such as an illumination system that conditions a beam ofradiation and a mask 71 that is illuminated with the beam of radiation72 from the source 70. A projection system 73 is provided to project thebeam of radiation onto the substrate 74. However, as described above, arotatably mounted mirror 75 is provided that is configured to adjust theposition of the patterned beam of radiation 76 that is projected ontothe substrate 74 relative to the projection system 73. An actuatorsystem 77 is provided to control the movement of the rotatably mountedmirror 75. For clarity in FIG. 10, the rotatably mounted mirror 75 isdepicted after the projection system 73. However, it should beappreciated that the rotatably mounted mirror may be part of theprojection system 73 or may be provided prior to the projection system.In addition, one or more additional rotatably mounted mirrors may beprovided to improve control of the movement of the patterned beam ofradiation relative to the projection system. Likewise it will beappreciated that any other mechanism may be used to adjust the positionof the patterned beam of radiation relative to the projection system.

Measurement systems 78, 79 are provided to measure the movement of themask 71 and substrate 74 (and/or of their support structures or tables),respectively. Based on these measurements, a controller 80 may determinethe desired adjustment of the position of the patterned beam ofradiation 76 relative to the projection system 73 in order to compensatefor the deviation in the intended relative movement of the mask 71 andthe substrate 74, taking into account the magnification of theprojection system 73, as required. Accordingly, the required signals areprovided to the actuator 77 to adjust the position of the patterned beamof radiation 76 relative to the projection system 73.

While specific embodiments of the invention have been described above,it will be appreciated that the invention as claimed may be practicedotherwise than as described. For example, although use of a lithographyapparatus to expose a resist on a substrate is he rein described, itwill be appreciated that the invention is not limited to this use, andan apparatus according to an embodiment of the invention may be used toproject a patterned radiation beam for use in resistless lithography..Thus, it is explicitly noted that the description of these embodimentsis not intended to limit the invention as claimed.

1. A lithographic projection apparatus, comprising: a projection systemconfigured to project a patterned radiation beam onto a target portionof a substrate; a positioning structure configured to move the substraterelative to the projection system during exposure by the patternedradiation beam; a pivotable mirror configured to move the patternedradiation beam relative to the projection system during at least onepulse of the patterned radiation beam; and an actuator configured tooscillatingly pivot the mirror according to an oscillation timing thatsubstantially corresponds to a pulse frequency of a radiation system andsuch that the patterned radiation beam is scanned in substantialsynchronism with the movement of the substrate during the at least onepulse.
 2. The apparatus of claim 1, wherein the actuator is controlledby a controller, wherein the controller, actuator and radiation systemare interconnected in a control loop arrangement, and wherein thecontrol loop is configured to maintain substantial synchronism betweenoscillation of the mirror and pulses of the radiation system.
 3. Theapparatus of claim 1, wherein the pivotable mirror is supported by asupport assembly, and a frequency of the oscillation timingsubstantially corresponds to a resonance frequency of the mirror and itssupport assembly.
 4. The apparatus of claim 3, wherein the supportassembly further comprises the actuator.
 5. The apparatus of claim 4,wherein the support assembly further comprises a counter-massconstructed and arranged to isolate forces produced by the actuator froma remaining part of the apparatus.
 6. The apparatus of claim 1, whereinthe actuator comprises a plurality of motors, constructed and arrangedto impart rotational forces on the mirror.
 7. The apparatus of claim 1,wherein, when in use, the mirror oscillates with a sinusoidal motion. 8.The apparatus of claim 7, wherein, when in use, the pulses of theradiation system substantially correspond in timing to a zero crossingof the sinusoidal motion of the mirror oscillation.
 9. The apparatus ofclaim 1, wherein, when in use, a position of the patterned radiationbeam relative to the projection system can be further shifted in orderto compensate for an error of movement of the substrate during a pulseof the patterned radiation beam.
 10. The apparatus of claim 1, whereinthe actuator is configured such that it can control a position of amid-point of an oscillation of the pivotable mirror.
 11. The apparatusof claim 10, wherein the pivotable mirror is configured to oscillateabout a first axis and the actuator is configured to control an angularposition of the mid-point of the oscillation of the pivotable mirrorabout the first axis.
 12. The apparatus of claim 10, wherein thepivotable mirror is configured to oscillate about a first axis and theactuator is configured to control an angular position of the mid-pointof the oscillation of the pivotable mirror about a second axis, thesecond axis being substantially perpendicular to the first axis andlying in a plane substantially parallel to a surface of the pivotablemirror at a location on which the patterned radiation beam would beincident on the pivotable mirror.
 13. The apparatus of claim 1, whereinthe actuator is configured to control a relative phase of a pulsefrequency of the radiation system and an oscillation of the pivotablemirror.
 14. The apparatus of claim 1, wherein the actuator isconstructed to oscillatingly pivot the pivotable mirror relative to abase of the actuator, and further comprising a second actuatorconfigured to control the position of the base relative to theprojection system.
 15. The apparatus of claim 14, wherein the actuatoris configured to oscillate the pivotable mirror about a first axis andthe second actuator is configured to control an angular position of thebase relative to the projection system about a second axis, the secondaxis being substantially parallel to the first axis.
 16. The apparatusof claim 14, wherein the actuator is configured to oscillate thepivotable mirror about a first axis and the second actuator isconfigured to control an angular position of the base relative to theprojection system about a third axis, the third axis being substantiallyperpendicular to the first axis and lying in a plane substantiallyparallel to a surface of the pivotable mirror at a location on which thepatterned radiation beam would be incident on the pivotable mirror. 17.The apparatus of claim 14, wherein the second actuator comprises aLorentz actuator and is configured to minimize transfer of a vibrationfrom the actuator to the remainder of the lithographic projectionapparatus.
 18. The apparatus of claim 1, wherein the mirror issubstantially planar.
 19. The apparatus of claim 1, wherein the mirroris located proximate a pupil plane of the projection system, or aconjugate plane thereof.
 20. The apparatus of claim 1, wherein themirror is located at a conjugate plane of a pupil plane of theprojection system.
 21. The apparatus of claim 1, wherein the positioningstructure is configured to move the substrate at a substantiallyconstant velocity relative to the projection system during a pluralityof pulses of the patterned radiation beam and during intervalstherebetween, and wherein, when in use, the patterned radiation beam ismoved in substantial synchronism with movement of the substrate for aduration of at least one pulse of the patterned radiation beam.
 22. Theapparatus of claim 1, wherein, when in use, the patterned radiation beamis scanned in substantial synchronism with movement of the substrateduring a plurality of pulses of the patterned radiation beam, such thata pattern is projected onto substantially a same place on the substratea plurality of times.
 23. The apparatus according to claim 22, wherein(i) an intensity of the patterned radiation beam, (ii) an illuminationof a programmable patterning structure, (iii) a pupil filtering, or (iv)any combination of (i) to (iii), are changed for at least one of aplurality of projections of the patterned radiation beam that aredirected onto substantially the same place on the substrate.
 24. Theapparatus of claim 1, wherein, when in use, a configuration of a patternis changed between a plurality of projections of the patterned radiationbeam that are directed onto substantially the same place on thesubstrate.
 25. The apparatus of claim 1, comprising a controllerconfigured to control motion of the mirror, the controller comprising: areference signal generator configured to generate a reference signalcorresponding to a desired motion of the mirror; a sensor configured tomeasure an actual motion of the mirror; and a signal compensatorconfigured to adjust the reference signal to generate a compensatedsignal, based on a phase difference between the measured motion of themirror and the desired motion, the compensated signal used to controlthe actuator.
 26. The apparatus of claim 25, wherein the signalcompensator is further configured to adjust the reference signal togenerate the compensated signal based on a measured amplitude differencebetween the measured motion of the mirror and the desired motion,represented by the reference signal.
 27. The apparatus of claim 1,comprising a controller configured to control motion of the mirror, thecontroller comprising: a reference signal generator configured togenerate a reference signal corresponding to a desired motion of themirror; a sensor configured to measure an actual motion of the mirror;and a resonant frequency adjustment unit configured to adjust theresonant frequency of oscillation of the mirror in response to a phasedifference between the measured motion of the mirror and the desiredmotion.
 28. The apparatus of claim 27, wherein the mirror is supportedby a flexible support and the resonant frequency adjustment unit isconfigured to control a stiffness of the flexible support.
 29. Theapparatus of claim 28, wherein the flexible support comprises a chambercomprising a magneto-rheological fluid, and the resonant frequencyadjustment unit is configured to control a magnetic field applied to thechamber.
 30. The apparatus of claim 27, wherein the resonant frequencyadjustment unit is constructed such that it can adjust the mass of themirror, or of a support that supports the mirror, or of both the mirrorand the support.
 31. The apparatus of claim 30, wherein the mirror, orthe support, or both the mirror and the support comprises a chamber, andthe resonant frequency adjustment unit is configured to control anamount of liquid within the chamber.
 32. A device manufacturing method,comprising: moving a substrate relative to a projection system thatprojects a patterned radiation beam onto a substrate during exposure;oscillatingly pivoting a pivotable mirror according to an oscillationtiming that substantially corresponds to a pulse frequency of thepatterned radiation beam so as to alter a path of the patternedradiation beam in substantial synchronism with movement of thesubstrate; and projecting the patterned radiation beam onto thesubstrate.
 33. The method of claim 32, wherein moving the substrateincludes moving the substrate at a substantially constant velocityrelative to the projection system during a plurality of pulses of thepatterned radiation beam and during intervals therebetween, and whereinthe path is altered in substantial synchronism with the movement of thesubstrate for a duration of at least one pulse of the patternedradiation beam.
 34. The method of claim 32, further comprising alteringthe path of the patterned radiation beam in substantial synchronism withthe movement of the substrate during a plurality of pulses of thepatterned radiation beam, such that a pattern is projected ontosubstantially a same place on the substrate a plurality of times. 35.The method of claim 34, further comprising changing a configuration ofthe pattern between a plurality of projections of the patternedradiation beam that are directed onto substantially the same place onthe substrate.
 36. The method of claim 34, further comprising changing(i) an intensity of the patterned radiation beam, (ii) an illuminationof a programmable patterning structure, (iii) a pupil filtering, or (iv)any combination of (i) to (iii), for at least one of the plurality ofprojections that are directed onto substantially the same place on thesubstrate.
 37. The method of claim 32, wherein the mirror oscillateswith a sinusoidal motion.
 38. The method of claim 37, wherein pulses ofthe patterned radiation beam substantially correspond in timing to zerocrossings of the sinusoidal motion of the mirror.
 39. The method ofclaim 32, wherein the path of the patterned radiation beam is furthershifted in order to compensate for an error of movement of the substrateduring a pulse of the patterned radiation beam.
 40. An apparatuscomprising a projection system, the projection system having: apivotable mirror configured to receive a patterned beam of radiation;and an actuator functionally connected to the pivotable mirror andconfigured to oscillatingly pivot the mirror.
 41. The apparatus of claim40, wherein the pivotable mirror is positioned in a pupil plane of theoptical system, or a conjugate plane thereof.
 42. The apparatus of claim40, wherein the actuator is configured to oscillate the mirror at afrequency in the range of 1-10 kHz.
 43. The apparatus of claim 40,further comprising a radiation source; and a patterning deviceconstructed and arranged to receive a radiation beam provided by theradiation source and to pattern the radiation beam.
 44. The apparatus ofclaim 43, wherein the patterning device is a programmable patterningdevice.
 45. A lithographic apparatus comprising: an illumination systemconfigured to condition a radiation beam; a support constructed to holda patterning device, the patterning device configured to impart theradiation beam with a pattern in its cross-section to form a patternedradiation beam; a substrate table constructed to hold a substrate; aprojection system configured to project the patterned radiation beamonto a target portion of the substrate; a position measurement systemconfigured to measure a position of the patterning device, or of thesupport, or of both the patterning device and the support; a positionmeasurement system configured to measure a position of the substrate, orof the substrate table, or of both the substrate and the substratetable; and a radiation beam position adjuster configured to adjust aposition of the patterned beam of radiation projected onto thesubstrate, relative to the position of the projection system, inresponse to a deviation of the measured relative position of thepatterning device and the substrate from an intended relative positionof the patterning device and the substrate.
 46. The apparatus of claim45, wherein the radiation beam position adjuster includes a pivotablemirror configured to move the patterned beam of radiation relative tothe projection system, and an actuator configured to control a positionof the mirror.
 47. A device manufacturing method, comprising: patterninga beam of radiation with a patterning device; projecting the patternedbeam of radiation, using a projection system, onto a target portion of asubstrate to form an exposure; measuring the position of the patterningdevice, of a support holding the patterning device, or of both thepatterning device and the support, during the exposure; measuring theposition of the substrate, of a table holding the substrate, or of boththe substrate and the table, during the exposure; and adjusting aposition of the patterned beam of radiation projected onto thesubstrate, relative to the projection system, in response to a deviationof the measured relative position of the patterning device and thesubstrate from an intended relative position of the patterning deviceand the substrate.
 48. The method of claim 47, comprising moving apivotable mirror to move the patterned beam of radiation relative to theprojection system.